1. Field of the Invention
The present invention relates to signal processors for processing information signals retrieved from a magnetic storage medium, and in particular, to neural network based signal processors for partial response maximum likelihood (PRML) read channels.
2. Description of the Related Art
Referring to FIG. 1, a conventional data storage and retrieval system which uses a magnetic disk includes a write channel and a read channel. Within the write channel, user data 9 is encoded by a data encoder 10 (e.g., with some form of run length limited code). The encoded data 11 is converted into a data symbol sequence by a data sequencer 12 (translating logic 0 bits to -1 and logic 1 bits to +1). The resulting data sequence 13 is stored on a magnetic disk 14d via the disk read/write electronics 14a, actuator arm 14b and read/write head 14c.
Within the read channel, the information signal 15 retrieved from the disk (via the read/write head 14c, actuator arm 14b and read/write circuit 14a) is filtered by a filter 16 and the filtered signal 17 is buffered by a gain controlled buffer amplifier 18. The buffered analog signal 19 is converted to a digital signal 21 by an analog-to-digital converter, or sampler, 20 and filtered by an equalizing filter 22. The equalized sample sequence 23 is used by a gain and timing control circuit 24 for controlling the gain of the buffer amplifier 18 via a gain control signal 25a and for controlling the sampler 20 via a sample control signal 25b. The equalized sample sequence 23 is also processed by a Viterbi detector 26 to determine the correct data sequence. This detected signal 27 is decoded by a data decoder 28 to provide the user data 29.
In such a conventional PRML read channel, a high sampling rate for the data is required to capture the signal samples, and with increasingly higher data retrieval rates such sample rates are now typically quite high. Accordingly, to keep up with such high speed data sampling, high speed hard wired digital signal processors (DSPs) must often be used.
Accordingly, it would be desirable to have a data read channel which avoids the need for high speed samplers and DSPs.